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Fair Value and Carrying Value of Financial Instruments and Long-Term Debt (Detail) - USD ($) $ in Thousands	Nov. 30, 2015	May. 31, 2015	Nov. 30, 2014	May. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, carrying value	$ 190,609	$ 174,711	$ 296,527	$ 332,868
Marketable equity securities, carrying value	125,628	131,866
Marketable debt securities, carrying value	22,787	22,904
Long-term debt, including current portion, carrying value	1,676,064	1,656,075
Cash and cash equivalents, fair value	190,609	174,711
Marketable securities, fair value	148,415	154,770
Long-term debt, including current portion, fair value	1,724,147	1,783,962
Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities, fair value	125,628	131,866
Fixed maturity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities, fair value	$ 22,787	$ 22,904